Rubicline is a very rare rubidium-rich member of the feldspar group, structurally related to microcline. It is prized by advanced mineral collectors for its distinct reddish to pinkish coloration resulting from rubidium substitution. It is primarily found in highly evolved granite pegmatites associated with other rare-element minerals.
Is this rubicline?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch rubicline with a known reference. Rubicline sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: prismatic crystals.
Often confused with
Rubicline vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside rubicline
Minerals reported to co-occur with rubicline. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- RbAlSi₃O₈
- Mohs hardness
- 6
- Density
- 2.58 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Prismatic crystals
- Cleavage
- Perfect on {001}, good on {010} (by analogy to microcline)
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In the core zones of complex Li-Cs-Rb-enriched, rare-element, granitic pegmatites, by exsolution from a K-Na-Rb-enriched precursor, followed possibly by fluid-induced modification
Where rockhounds find rubicline
Classic worldwide localities
- San Piero in Campo, Elba, Italy
Field-hunting tip
Where it forms: In the core zones of complex Li-Cs-Rb-enriched, rare-element, granitic pegmatites, by exsolution from a K-Na-Rb-enriched precursor, followed possibly by fluid-induced modification. If you start seeing rubidian microcline, albite, muscovite in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify rubicline?+
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What rocks look like rubicline?+
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Find rubicline on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
